1. Field of the Invention
The present invention relates to a swash plate compressor and a piston therefor.
2. Description of the Related Art
A piston of a swash plate compressor is provided with an engagement portion for engaging with a swash plate. The engagement portion is typically provided with a pair of arm portions extending in parallel to each other and a coupling portion for coupling base ends of the arm portions each other. The coupling portion crosses over an outer circumference part of the swash plate, and the pair of arms engage with both surfaces of the swash plate via shoes, respectively. The coupling portion of the engagement portion receives bending moment when the swash plate compressor is activated. The piston is provided with an engagement portion and a head portion integrally. When the swash plate compressor is activated, the head portion reciprocatingly moves within a cylinder bore. Then, a force acts in the direction of forcing one of the pair of arm portions to move away from the other based on an inertial force acting on the head portion and a frictional force between an outer circumferential surface of the head portion and an inner circumferential surface of the cylinder bore, and bending moment acts in the direction of bending the coupling portion convexly toward the swash plate side.
The bending moment repeatedly acts a large number of times, which tends to cause fatigue fracture in the engagement portion, and therefore is a factor behind the decrease of durability of the piston. In order to improve the durability, it is sufficient to increase bending strength of the coupling portion. However, an attempt to increase the bending strength makes the piston heavier, and requirement of lightening the piston cannot be satisfied.
In addition, in order to increase the bending strength of the coupling portion, it is necessary to make a section modulus of a transverse section shape of the coupling portion larger. For this purpose, it is effective to make the coupling portion thicker. However, since the coupling portion is for coupling the pair of arm portions through a space between an outer circumferential surface of the swash plate and an inner circumferential surface of a housing, it is necessary to either making a diameter of the swash plate smaller or making a diameter of the housing larger to make the coupling portion thicker, both of which are not preferable.
The present invention has been devised in view of the above and other drawbacks, and it is an object of the present invention to provide a swash plate compressor and a piston therefor that are capable of at least one of increasing bending strength of a coupling portion to be increased while avoiding increasing weight of the piston as much as possible, and increasing a section modulus of the coupling portion without necessitating decrease of a diameter of a swash plate and increase of a diameter of a housing.
A piston for a swash plate compressor in accordance with the present invention is provided with a head portion to be fitted in a cylinder bore and an engagement portion, integrally formed with the head portion, which has a pair of arm portions and a coupling portion for coupling base ends of the arm portions each other and engages with a swash plate while crossing over a circumference part of the swash plate. The engagement portion is provided with a protruding portion that protrudes radially outwardly from a back surface on the opposite side of a swash plate side of the coupling portion.
The protruding portion may include an axial rib extending in a direction parallel to a central axis of the head portion on the back surface on the opposite side of the swash plate side of the coupling portion.
In addition, a swash plate compressor in accordance with the present invention is provided with the above-mentioned piston for a swash plate compressor, a housing having a cylinder bore which is fitted in the head portion of the piston and forms an accommodating recess capable of accommodating the protruding portion on the inner circumferential surface, and a swash plate for reciprocatingly moving the piston by converting its rotational motion about a rotation axis into the reciprocating motion of the piston while engaging with the engagement portion and inclining with respect to the rotation axis.